In a WCDMA (Wideband Code Division Multiple Access) radio communication system, a mobile station can simultaneously perform voice communication according to circuit switching and data communication according to packet switching. Some mobile stations are connected to a network to always transmit and receive data for them. These mobile stations are referred to as “always-connected terminals”.
An always-connected terminal may maintain a radio link even though no packet communication occurs. This radio link is referred to as a “PS (Packet Switched) bearer”. When a voice call is originated or received in this situation, a voice bearer is added and consequently a multi-call condition is raised. The voice bearer is referred to as a “CS (Circuit Switched) bearer”. In a multi-call condition, both radio resources for a PS bearer and radio resources for a CS bearer are consumed.
In order to reduce waste of radio resources, it is assumed that a PS bearer is released according to CSFB (Circuit Switched FallBack) for switching from a LTE (Long Term Evolution) network to a 3G network when a voice call is originated or received (see Japanese Patent Laid-Open Publication No. 2011-205403).